The present disclosure relates generally to the field of ophthalmics, more particularly to ophthalmic devices, including intraocular lenses (IOLs) such as accommodating intraocular lenses.
A healthy young human eye can focus an object in far or near distance, as required. The capability of the eye to change back and forth from near vision to far vision is called accommodation (see for example, Burd et al.
“Mechanics of accommodation of the human eye” Vision Research 39:1591-1595 (1999); Chien et al. “Analysis of human crystalline lens accommodation” J. Biomech. 39:672-680 (2006)). Accommodation occurs when the ciliary muscle contracts to thereby release the resting zonular tension on the equatorial region of the capsular bag of the eye. The release of zonular tension allows the inherent elasticity of the lens capsule to alter to a more globular or spherical shape, with increased surface curvatures of both the anterior and posterior lenticular surfaces.
When the ciliary muscle is relaxed, the ciliary muscle moves into the disaccommodated configuration, which is posterior and radially outward from the accommodated configuration. The radial outward movement of the ciliary muscles creates zonular tension on the lens capsule to stretch the equatorial region of lens toward the sclera. The disaccommodation mechanism flattens the lens and reduces the lens curvature (both anterior and posterior). Such natural accommodative capability thus involves altering the shape of the lens to the appropriate refractive parameters for focusing the light rays entering the eye on the retina to provide both near vision and distant vision.
Intraocular lens implantation for cataracts is the most commonly performed surgical procedure in elderly patients in the U.S., Nearly three million cataract surgeries are performed each year in the U.S., with an additional 2.5 million surgeries in Europe and Asia. In conventional extracapsular cataract surgery, the crystalline lens matrix is removed leaving intact the thin walls of the anterior and posterior capsules—together with zonular ligament connections to the ciliary body and ciliary muscles. The crystalline lens core is removed by phacoemulsification through a curvilinear capsularhexis and replaced with an intraocular lens. Unfortunately, conventional IOL's, even those that profess to be accommodative, may be unable to provide sufficient axial lens spatial displacement along the optical axis or lens shape change to provide an adequate amount of accommodation for near vision.
Several attempts have been made to make intraocular lenses that provide the ability to accommodate. However, there is still a need for an accommodative intraocular lens that can adequately change shape to simulate the action of a natural lens.